We are going to hear a lot about a new paper from the Jerry Silver at Case Western. Silver
, a former member of the Reeve Science Advisory Council, is a career spinal cord injury investigator. He’s opinionated and can come across as brashly confident, but he is a delightful character and also one of the most optimistic scientists in the field.
If you follow Jerry, who appears at all the major science meetings, including the Working to Walk conference in the fall, and who sometimes takes on Wise Young with mano a-mano swagger at the CareCure
website, then you will have heard a sneak preview of this new work for almost a year. Silver presented preliminary data last fall at the Society for Neuroscience meeting.
As a precedent, Silver published a Reeve-Foundation funded paper two years ago, a big advance in regenerative medicine (“Functional Regeneration of Respiratory Pathways After Spinal Cord Injury
”), showing that a bypass graft and a little shot of an anti-scar enzyme facilitated “remarkable recovery of diaphragmatic function” in paralyzed animals. A very cool science story, and it generated some headlines.
Herewith the new paper, showing functional bladder recovery from regenerated nerves after a complete T8 injury, facilitated by a bridge made of about 18 small peripheral nerves as a detour around the damage, nurtured by growth factors and powered by chondroitinase, the enzyme that unblocks scar tissue.
The paper, in the Journal of Neuroscience, is titled “Nerve Regeneration Restores Supraspinal Control of Bladder Function after Complete Spinal Cord Injury.” Silver worked with scientists from the Cleveland Clinic, including lead author of the paper, Yu-Shang Lee. I got a draft (bootlegged from a reporter in Cleveland, Silver’s hometown, soliciting comment from Reeve Senior VP Susan Howley). It was embargoed, as the term goes, until today.
So you know, supraspinal means from above the level of injury – from the brain. That means certain signals that affect the bladder got past the gap in the cord, by way of the surgical bridge; some axons, according to the paper, grew “remarkably” long distances and restored proper behavior of the lower urinary tract – not quite normal but quite good.
From the paper:
Here we used adult rats with complete thoracic cord transections that have been bridged by a combination of multiple peripheral nerve autografts (PNGs) covered by an acidic fibroblast growth factor (aFGF)-laden fibrin matrix plus ChABC [aka chase] delivered to the graft and at the graft/host interfaces. We provide physiological, anatomical, and pharmacological evidence of a surprising degree of regeneration from particular brainstem centers past the distal graft/cord interface, with some axons reaching all the way to lumbo-sacral levels and with return of bladder control.
Here’s what they did. Seven groups of 16 rats got different treatments. (Important to note, these are acute treatments. Silver’s group believes the strategy will work with chronic SCI too but that’s not what this is.) One group got just a laminectomy (a sham, no paralysis, used as a control). One group got a spinal cord transaction only (two cuts, removing 2 mm of spinal cord) and no treatment. Other groups got the same 2mm transection along with treatments variations including nerve graft only; nerve graft plus chase; nerve graft plus acidic fibroblast growth factor (aFGF); nerve graft plus chase and aFGF; chase and aFGF but no graft.
Three to six months after the surgeries, and the spinal cord injuries, the team began measuring urine output from all the animals, using a special cage that recorded frequency of voiding, and volume. They also ran a lot of bladder dynamics tests, electrophysiology tests, and later, anatomical studies to see what occurred.
They kept score by the number of times an animal was able to pee in a set amount of time, and by weight of bladder. As expected, the transaction animals (no treatment, totally paralyzed) were at the lowest level of voids, highest level of bladder weight. The sham group (not paralyzed) was at the top in voids, lowest in weight. What the scientists found was that each of the treated groups had better bladder function than those with no treatment but that the group with the nerve graft, chase and aFGF was significantly better than the others, even more so after six months. Improvement over time, they suggest, is due to the time it takes for nerves to regenerate.
Why is this? Chase breaks the scar but the success might have a lot to do with the aFGF. From the paper:
Why did this particular combination therapy [chase, aFGF and nerve graft] allow for such robust axonal regeneration well beyond that of our previous studies in which we used ChABC [chase] and single, longer bypass PNS bridges that were directed just above ventral horn gray matter? We suggest that maximizing surface area with the use of multiple grafts coupled with the enzyme effectively increases access to the distal white matter, which, in turn, can permit long-distance regeneration. In addition, the use of FGF may have a variety of beneficial synergistic effects. The FGF family members have multiple functions, including their capacity to modulate cell proliferation, migration, differentiation, and survival. Therefore, the application of aFGF in our repair strategy is important not only to facilitate axonal growth in general but also to help allow axons to grow straight, especially at the entrances and exits of the PNG.
Silver's group thinks the FGF may help by altering production of inhibitory factors at the site of growing axons, thus allowing them grow more easily in the area of damage.
Was there any other functional recovery? Not much. From the paper:
We have identified a subset of neurons situated primarily within the brainstem and reticular formation (and which are known to play important roles in bladder function)) as well as the propriospinal system that can regrow lengthy axons once a permissive environment that allows them past the glial scar is provided. We saw no evidence of regeneration by cortico-spinal or rubro-spinal axons (unlike the results by Cheng et al., 1996), which is one possible reason for the limited recovery of locomotor function (Basso–Beattie–Bresnahan score improved from 2 to 7 in the triple-combination).
So what happened? Some types of long axons apparently grew the length of the spinal cord (granted, in a rat, that's not very far). There may also have been a rewiring of the thickly woven network of shorter axons in the cord. The central pattern generator, which is involved in stepping and treadmill training, may have kicked in too. The scientists do know that the recovery of bladder function was related to restoration of brain input; by recutting the spinal cords of the treated animals, the gains in bladder function disappeared.
There is a lot more to know. From the paper:
The current study provides an experimental framework for stimulating functional regeneration after acute severe SCI. Micturition control is complex and recovery takes a long time, but, rather remarkably, it would appear that certain primitive brainstem-mediated functions lost to SCI such as respiration and urination do possess the capacity to rewire themselves even when a relatively small number of axons can be induced to regenerate beyond the glial scar. However, and importantly, we do not yet know precisely how many and where beyond the lesion the functionally relevant synapses need to be re-formed. The critical synapses may occur within the interneuronal pool just beyond the graft in which most fibers end.
The future challenge will be to provide even more favorable environments and increase the intrinsic growth potential of these particular supraspinal neurons to facilitate more substantial and rapid axonal regeneration to further enhance recovery of these but also other systems not only after acute but also after chronic SCI.
The novel combination treatment allows for remarkably lengthy regeneration of certain subtypes of brainstem and propriospinal axons across the injury site and is followed by markedly improved urinary function. Our studies provide evidence that an enhanced nerve grafting strategy represents a potential regenerative treatment after severe spinal cord injury.